Office of Environmental Health & Safety

Mold and Indoor Air Quality

Mold is a type of fungi; the two terms are often used interchangeably. The kingdom of fungi includes mushrooms, molds, mildew, and yeasts. Fungi are part of the natural environment. Outdoors, fungi play a vital role in nature by breaking down dead organic matter (e.g. fallen leaves, dead trees), but indoors, mold growth should be avoided. Fungi reproduce by means of tiny spores; the spores are invisible to the unaided eye and float through outdoor and indoor air. Fungi may begin growing indoors when spores land on wet surfaces. All fungi need water/moisture in order to grow.

Molds and other fungi are found everywhere – both indoors and outdoors all year round. We are all constantly exposed to a wide variety of mold. Although most public-assembly buildings (e.g. campus buildings) have ventilation systems that filter out most mold spores, they find their way into indoor spaces through open windows, doors, on people’s clothing and shoes, and anything else carried into a building.

Once mold spores are present in the indoor environment, they remain dormant until conditions are favorable for reproduction and growth. Mold needs a food source (could be anything, but it is most often cellulose-containing), and a source of moisture (e.g. flood, high humidity, dampness). If left to proliferate, mold “blooms” can damage building materials, furniture and other items.

Molds have the potential to cause health problems, although the presence of mold does not always mean that health problems will occur. Molds produce allergens, irritants, and in some cases, potentially toxic substances (mycotoxins). Inhaling or touching mold or mold spores may cause immediate- or delayed allergic reactions in sensitive individuals. Allergic responses include hay fever-type symptoms, such as sneezing, runny nose, red eyes, and skin rash. Allergic reactions to mold are common. Molds can also cause asthma attacks in people with asthma who are allergic to mold. In addition, mold exposure can irritate the eyes, skin, nose, throat, and lungs of both mold-allergic and non-allergic people. Symptoms other than the allergic and irritant types are not commonly reported as a result of inhaling mold.

It is neither possible nor necessary to remove all mold spores from the indoor environment. Control of mold is most often about controlling moisture in the indoor environment. Leaks, floods, areas of condensation, high humidity, and dampness should be promptly discovered and corrected, and monitored for recurrence. Areas in which mold has proliferated should be promptly cleaned up, using a solution of soap/detergent and water, and wiped clean with a damp cloth and allowed to dry completely. Biocides (such as chlorine bleach) are usually not necessary, and not recommended.

If water intrusions are corrected, cleaned and completely dried within 24-48 hours, mold growth can be avoided entirely. Mold must be physically removed from a surface, not neutralized and left where it was found. Although it cannot reproduce, it is still present, as a particulate that may also contain mycotoxins. Absorbent materials (such as ceiling tiles & carpet) that become moldy may have to be replaced.

Generally, it is not necessary to identify the species of mold growing in a building. Measurements of mold in air are not reliable or representative. There are no regulatory standards for mold that can be used to determine compliance for mold exposure. If mold is seen or smelled, there is a potential health risk; therefore, no matter what type of mold is present, it should be removed.